Field of the Invention: Mountaineers, kayakers, cyclists, and other travelers who wish to minimize the weight they must carry often sleep in bivouac sacks rather than tents. Such bivouac sacks are typically formed of elongated fabric envelopes or enclosures that are sized and shaped to fully enclose one person inside a large sleeping bag and provide extra volume around the person's head. In the past, the top sheet of fabric has consisted of two pieces that overlap generally near the chest area to enable ingress and egress. The overlap is usually sufficient to minimize entry of precipitation, but not enough to fully prevent it. Providing enough ventilation to the interior of the bivouac sack without allowing large amounts of precipitation to enter is essentially impossible with such designs.
An alternative means of entry has been provided in the some bivouac sacks wherein an opening is formed, either along the margin at the head end or along the margin at the side. Here again, this design fails to provide enough ventilation while preventing the entry of precipitation during periods of rain or snow.
Existing bivouac sacks provide only a minimal amount of adjustability in the amount of ventilation provided to the interior. In most cases, a zipper used to close the sack is the only available means user has for adjusting the size of the opening and controlling ventilation. This method, however, requires the user to pull the top of the sack back from the head to allow more ventilation, thus exposing the user's head to the elements. While mosquito netting can be used to block insects, the user's head is still subject to precipitation and the elements.
Hence, there is a need for a portable bivouac shelter that enables selective positioning of the top sheet of the sack and holding of the top sheet in either a partially open or fully open position while still protecting the user's head. It is further desirable that such a shelter allow a user to reposition the opening while remaining inside the shelter and without having to remove mosquito netting or otherwise exposing the user to the elements.